1, vitamin A has to promote growth, reproduction, maintenance of bones, epithelial tissue, vision and mucosal epithelium normal secretion of a variety of physiological functions, vitamin A and its analogues have to stop the role of pre-cancerous lesions.

Deficiency is manifested as growth retardation, diminished dark adaptation and the formation of night blindness. Dry eye disease occurs due to drying, desquamation, hyperkeratosis of epidermal and mucosal epithelial cells, and decreased secretion of lacrimal glands, resulting in blindness due to corneal softening and perforation in severe cases.

2. The main function of vitamin D is to promote the absorption of calcium and phosphorus in the mucosal cells of the small intestine. Calcium ion absorption in the intestine requires a calcium binding protein, 1,25-dihydroxyvitamin D3 can induce the synthesis of this protein, promote Ca2+ absorption, but also to promote the renewal of calcium salts and the generation of new bone, but also to promote the absorption of phosphorus and the renal tubular cells of calcium and phosphorus reabsorption, so it can improve the concentration of blood calcium and phosphorus, is conducive to the generation of new bone and calcification.

In addition, vitamin D also promotes skin cell growth, differentiation and regulation of immune function. General adult frequent exposure to sunlight does not occur deficiency disease, infants and young children, pregnant women, lactating mothers and infrequent outdoor activities of the elderly to increase the supply of vitamin D to 10 μg per day (equivalent to 400 international units). Lack of vitamin D children can suffer from rickets, adults suffer from osteomalacia.

Extended information:

Source of vitamin D:

Vitamin D are made of corresponding vitamin D proteins transformed by ultraviolet light. Vitamin D proteins are cyclopentane polyhydrophenanthrene compounds. The 5,7 position in the B ring of vitamin D is a double bond, which can absorb light quanta at 270-300nm, thus initiating a series of complex photochemical reactions leading to the formation of vitamin D. If the vitamin D is ergocalciferol, the photoproduct is vitamin D2, and if the vitamin D is 7-dehydrocholesterol, the photoproduct is vitamin D3.

Vitamin D2 is also called ergocalciferol, is synthesized mainly from plants, yeast, ergot, etc. are more abundant. Vitamin D3, also known as cholecalciferol, the epidermis and skin tissues of most higher animals contain 7-dehydrocholesterol, as long as sunlight or ultraviolet light irradiation by photochemical reaction can be converted to vitamin D3. Vitamin D3 is mainly found in marine fish, animal liver, egg yolks and lean meats, skim milk, cod liver oil, cheese, nuts and seafood. Both types of vitamin D have the same physiological role. The human body obtains the vitamin mainly from the body's own synthesis and from animal foods

Baidu Encyclopedia - Vitamin A

Baidu Encyclopedia - Vitamin D